This chapter presents the Cisco Voice Interworking Service Module (VISM) set of features and the solutions provided by this voice card, including Voice Over AAL2, Voice over ATM, and Voice over IP (VoIP) networks.

This chapter is from the book

This chapter is from the book

This chapter presents the Cisco Voice Interworking Service Module (VISM) set
of features and the solutions provided by this voice card, including Voice Over
AAL2, Voice over ATM, and Voice over IP (VoIP) networks. This chapter shows you
how to add, configure, display, and verify voice connections. It describes VISM
clocking, including clocking options and configuration procedures.

Multiprotocol Label Switching (MPLS) is introduced, with the steps required
to set up MPLS on the RPM. The MPLS section does not provide detailed
configuration information; it is intended only as a guide for planning for MPLS
in your network.

The RPM, including memory locations and port numbering, is also described,
and the Cisco IOS command-line interface is introduced. Commands for configuring
the RPM and for setting up the RPM ATM switch interface are explained. This
chapter also discusses permanent virtual circuits (PVCs) on the RPM, including
commands for creating and displaying these PVCs.

VISM Overview

The first key topic discussed in this chapter is the Cisco Voice Interworking
Service Module (VISM). The VISM consists of a front and back card set designed
to operate on the Cisco MGX 8250/8850-PXM1 switches for Releases 1.5 and 2.0.
For VISM services on MGX 8230 switches, you must use VISM Release 2.0 or 2.1.
The VISM provides interfaces to an ATM packet network and to TDM (time-division
multiplexing) T1/E1 lines.

VISM Release 2.1 is a single-height Cisco MGX front card. As many as 24 cards
can be installed in a Cisco MGX 8250 or Cisco MGX 8850 shelf, and as many as 8
cards can be installed in a Cisco MGX 8230 shelf. Each VISM supports either
eight T1 lines or eight E1 lines. There are two hardware versions of the
cardone for T1 lines and one for E1 lines. T1 and E1 lines cannot be mixed
on a VISM card. (VISM is not supported on the Cisco MGX 8260 platform.)

A Cisco MGX 8850 Wide Area Edge Switch, when equipped with one or more VISM
card sets, can transport digitized voice signals across a packet network. Thus,
the VISM/MGX 8850 combination provides an interface or gateway between
conventional voice TDM networks and networks based on packet-switching
technology.

VISM employs the concept of operating modes, which permit it to be used in a
variety of applications. Releases 1.5 and 2.0 have two operating modesVoIP
and AAL2 trunking. These modes support three major applications:

SwitchingUsing VoIP mode, this application provides the
emulation of many of the functions of a tandem (Class 4) switch. In this
application, VISM functions as voice gateway (also called a media gateway) to an
IP network and performs call control in conjunction with a call agent. The call
agent (also called a media gateway controller) initiates and controls the call
control functions. VISM transmits the voice payload through a bearer circuit
using VoIP and ATM AAL5 network protocols.

Multiservice Access with Call ControlThis application also
uses VoIP mode. In this application, the VISM/MGX 8850 combination is used to
concentrate voice and user data services onto a single broadband circuit for
transmission over the packet network, again using VoIP and ATM AAL5 techniques.
As with the switching application, VISM can function with a call agent to
perform call control. In this application, VISM can function as a front-end to a
voice gateway.

AAL2 trunkingThis application uses AAL2 trunking mode. In
this application, a VISM/MGX 8850 combination is used to concentrate voice (and
fax/modem) user services over a preprovisioned AAL2 trunk. VISM merely passes
(tunnels) bearer and signaling data across a packet network. It plays no part in
call setup and teardown.

VISM architecture provides the following benefits:

Technology flexibility that allows the incorporation of new or improved
technology as it becomes available

Application flexibility such that it can be used in a range of
situations, providing interoperability with a wide variety of equipment
types

Modularity that allows equipment to be purchased and installed as it is
needed in a step-by-step manner